National meteorological early warning service for geological disasters

5.8. 1. 1 working conditions

From May/KLOC-0 to September 30, 2008, the national meteorological early warning and forecasting service for geological disasters was launched once a day. Due to Wenchuan earthquake, typhoon activity and heavy rainfall, the early warning and forecasting duty was strengthened and continued in 2008. After May 13, the frequency of prediction in earthquake-stricken areas was increased from 1 time per day to 2 ~ 3 times, an increase of 60 times. The early warning and forecasting period was also extended from September 30th to June 4th 10 (Typhoon Hagas made landfall), and on June 5th 1 1 time was increased for 6 days.

I was on duty for *** 159 days in 2008, and made 2 13 copies of early warning products. Geological disaster early warning and forecasting information was released 94 times in CCTV (including 93 times in Grade 4 and 94 times in Grade 5 1 time), 94 times in china national radio, 76 times in China Geological Environment Information Network (above Grade 3) and 94 times in the government website of the Ministry of Land and Resources.

Due to the loose and broken rock mass on the hillside in Wenchuan earthquake area, aftershocks continue and heavy rainfall occurs frequently, the early warning and prediction of geological disasters have been strengthened. It is mainly to increase the frequency of prediction and moderately improve the level of geological disaster prediction. The frequency of making geological disaster early warning and forecasting products increased from 1 time to 3 times a day, which were released on CCTV meteorological programs at 7: 00 a.m., noon 12 and 7: 30 p.m. respectively, and rolled with CCTV and china national radio meteorological programs, and released in real time on China Geological Environment Information Network. Warning local residents and emergency rescue and relief personnel to pay attention to prevent geological disasters such as landslides, collapses and mudslides caused by earthquake aftershocks and rainfall; Warn people who temporarily live in tents and disaster relief places, avoid places prone to geological disasters such as hillsides and river gullies, and remind vehicles and pedestrians driving along mountain roads to pay attention to landslides, falling rocks and mudslides.

The workflow of appropriately increasing the frequency of meteorological early warning and forecasting of geological disasters is: proposed by the National Meteorological Center and jointly released after consultation with China Geological Environment Monitoring Station. If it is predicted that the tropical storm will affect Chinese mainland after it is generated in the western Pacific, the National Meteorological Center will inform the Geological Environment Monitoring Institute of China in advance to make preparations for the meteorological early warning and forecast of geological disasters in the southeast coast.

5.8. 1.2 Calculation of Early Warning Products

(1) integrates two generations of early warning models.

In order to facilitate the parallel use and mutual verification of the old and new early warning models and improve the accuracy of the calculation results of early warning and forecasting, the first generation early warning model (critical rainfall model) and the second generation early warning model (explicit statistical early warning model) are integrated into the same system in the new early warning and forecasting system software (Figure 5.35).

First-generation early warning model (critical rainfall model): Geological disaster prediction based on rainfall station, where early warning calculation is completed and different early warning grade points are generated.

Second-generation early warning model (explicit statistical early warning model): calculate the early warning product value on each early warning grid with the divided grid (10km × 10km) as the unit.

Figure 5.35 Comprehensive use of two generations of early warning models

(2) step-by-step calculation and one-step calculation can be adopted.

Distributed computing is mainly divided into two steps: automatic import of meteorological data and calculation of forecast products, which is convenient for rainfall download, data import and data distribution view before calculation of early warning products (Figure 5.36). One-stop calculation: data import and product calculation are completed in one step from beginning to end, and daily early warning duty is convenient and fast.

Figure 5.36 Step-by-step calculation and one-stop calculation.

5.8. 1.3 data management

(1) rainfall data is automatically downloaded.

When the meteorological department uploads the previous live rainfall and the next day's forecast rainfall to the FTP address, whether it is one-stop calculation or distributed calculation, the first step for forecasters to use early warning software is to download the data directly from FTP, automatically prompt after downloading, and directly import it into the software system to participate in the calculation.

Regional early warning method of geological disasters in China and its application

(2) Automatic data backup

According to the needs of daily work, the software realizes the automatic backup of the original rainfall data and the results of early warning products after calculation (Figure 5.37).

Figure 5.37 Automatic data backup

Back up the original rainfall data to the directory "D: \2008rain\070 1"

Copyftp:/129.179.10.68/c-CMA/a-forecast/0701/the whole folder.

Back up the result data of early warning products to the directory "D: \2008results\070 1"

Copy 3 files under "Data \ Publishing":

gt 08070 1 . doc； gt 08070 1 . txt； 08070 1 . BMP； 08070 1 . jpg；

Copy three files 080701.wl under "Data \ Results"; 08070 1 . w p；

Copy "data \ station \08070 1.w t"

5.8. 1.4 data query

In terms of data query function, in addition to the query of geological background and environmental conditions (Figure 5.38, first open the geological environmental conditions data to be queried in the layer management bar, and then use "View Properties" to view the corresponding geological environmental conditions), this software improvement is mainly to add a more powerful rainfall data query function.

Rainfall query function is mainly based on the original query, statistical query and data export of rainfall stations. Right-click "station query" to get the information of each rainfall station, which mainly includes four tabs: actual rainfall, accumulated rainfall, rainfall at 14 hour and conditional query.

Figure 5.38 Query on Geological Background and Environmental Conditions

Actual rainfall: the query result is the daily 24-hour rainfall value of the selected rainfall station (Figure 5.39). The query result of accumulated rainfall is the daily accumulated rainfall of the selected rainfall station, and the system is designed as the accumulated rainfall of 7 days.

Figure 5.39 Rainfall Query Window

Rainfall at 14: the query results are the 6-hour live rainfall from 8: 00 to 14 and the calculated live rainfall from 14 to yesterday 14.

Conditional query: it mainly includes some complex user-defined query functions and query result export functions. By selecting station number, station name, start date and end date, you can query the accumulated rainfall of each rainfall station in different time periods (Figure 5.40).

Figure 5.40 Conditional Query

5.8. 1.5 Early warning product version

After the geological disaster early warning and forecasting products are automatically completed, forecasters can modify the early warning products according to experience or consulting results. On the basis of the revision of early warning products, the map of prone areas in different provinces has been added; The product background data supplemented the county boundary, county name and topographic map.

(1) Add maps of provinces (autonomous regions and municipalities) (Figure 5.4 1).

Figure 5.4 1 prone areas of provinces (autonomous regions and municipalities)

(2) The product background data (Figure 5.42, Figure 5.43) has been modified.

Figure 5.42 Geomorphological Basemap of China

Figure 5.43 Name of County Boundary in Early Warning Area

5.8. 1.6 software interface and display

The software interface is further improved; Layer display standardization, etc. For example, different rainfall is marked with different colors; The colors of different warning levels are also given corresponding color display standards.

(1) software interface

From the daily early warning duty, the interface of early warning software is further improved and simplified, and the layer control management window is clearer and more convenient to use (Figure 5.44).

Figure 5.44 Improved software interface

(2) Standardization of layer display

Different rainfall is marked with different colors and sizes. The relevant convention of rainfall display at 8 o'clock and 14 o'clock on the same day is based on the rainfall (sub-picture number is 34) (Figure 5.45):

Figure 5.45 Standardization of Real-time Rainfall Display at 8 o'clock

≥250mm: crimson (253), and RGB is1513123; The width and height of the subgraph are both 60;

100 ~ 250 mm: pink (183), RG B is 2550191; The width and height of the subgraph are both 50;

50 ~ 100 mm: blue (5), RG B is 0 0255; The width and height of the subgraph are both 40;

25 ~ 50 mm: light blue (19), RG B is135135 255; The width and height of the subgraph are both 30;

10 ~ 25mm: green (90), RG B is 01750; The width and height of the subgraph are both 20;

< 10 mm: light green (7), RG B is 0.2550; The width and height of the subgraph are both 10.

(3) color standardization of early warning level

(RGB, Figure 5.46)

Figure 5.46 Color Standardization of Early Warning Level

5.8. 1.7 Vectorization Online Publishing

Change the published early warning product format to vectorization format, and realize the convenient, fast and accurate positioning of early warning product query (you can directly query county-level administrative regions) (Figure 5.47). Real-time display and query of rainfall data can be realized according to needs; At the same time, it can meet the release requirements of early warning products many times a day.

Figure 5.47 Improved Vectorization Online Publishing and Magnification Effect

5.8.2 5 Grade Geological Disaster Warning Zone

In the flood season of 2008, * * * released 1 five-level warning and forecasting information. We investigated the occurrence of geological disasters predicted this time.

5.8.2. 1.5 Early warning and prediction of geological disasters

On the afternoon of July 20th, 2008, China Geological Environment Monitoring Station received the weather forecast from China Meteorological Bureau: in the next 24 hours (from 20: 00 on July 20th to 20: 00 on July 20th, 2 1), there will be heavy rain (50mm) in earthquake-affected areas such as southern Gansu, north-central Sichuan, southwestern Shaanxi and southern Ningxia. Among them, there are heavy rains (100mm) in southern Gansu, north-central Sichuan and southeast Jilin.

In view of the geological environment conditions in the rainfall forecast and rainstorm forecast areas of the Meteorological Bureau, after consulting with the provincial geological disaster early warning and forecasting technical units in the early warning areas and the Meteorological Bureau, the following early warning and forecasting information is hereby issued: from 20: 00 today to 20: 00 tomorrow, the earthquake-affected areas such as southern Gansu, north-central Sichuan, southwestern Shaanxi and southern Ningxia, as well as southeastern Jilin and eastern Liaoning are more likely to have geological disasters (level III). Among them, the possibility of geological disasters (magnitude 4 ~ 5) in earthquake-stricken areas such as southern Gansu, central Sichuan and northern Sichuan is greater or greater (Figure 5.48).

Fig. 5.48 isoline of rainfall forecast on July 20 and meteorological early warning and forecasting area of geological disasters

Geological disasters and geological environment in 5.8.2.2.

According to the feedback information obtained by the Department of Geology and Environment of Sichuan Province and the Department of Land and Resources of Gansu Province, there were 47 major geological disasters in southeastern Sichuan from the evening of July 20th to July 22nd. Eight geological disasters occurred in southern Gansu.

From July 20 to 22, the geological disasters in Sichuan Province were mainly distributed in the eastern and south-central parts of Sichuan Province. Geologically, they belong to the geological environment area of Huaying Mountain in the east of the basin and the geological environment area of Emei Mountain.

In the eastern part of the basin, the parallel geological environment area of Huaying Mountain Gully is dominated by denudation structure and landform, with anticlines forming mountains, synclines forming valleys, high mountains and deep valleys, alternating with valleys, and the mountain elevation is 700 ~1700 m, with limestone troughs or small intermountain basins in between. Intermountain basins are generally 300 ~ 500m above sea level, with a relative height difference of about100m ... The terrain slope is 30 ~ 35, and the anticline mountain area is steep. Jurassic is the most widely distributed (more than 80%). Stratigraphic lithology is mainly composed of soft and hard rock masses composed of mudstone, sandy mudstone, lithic feldspathic sandstone and siltstone with different thicknesses. The structure is NNE-NNE direction and consists of a series of parallel narrow asymmetric box anticlines with few faults. The regional crust is intermittent plane uplift with strong crustal activity. The maximum earthquake magnitude in this area is 5.75, and the basic earthquake intensity is ⅵ-ⅶ degrees.

The geological environment area of Emei Mountain is characterized by alpine landform, which gradually increases from north to south, with an altitude of1000 ~ 3,700 m, a cutting depth of 500 ~ 1000m, a topographic slope of 15 ~ 40, a gentle slope, a gentle top and a narrow valley. The strata include carbonate rocks and metamorphic rocks in Lower Paleozoic, sandstone, mudstone and volcanic eruption basalt in Mesozoic. There are many types of soft and hard rock mass combinations, and the rock mass is relatively broken. The structure is dominated by folds and faults in the north-south direction, and there are also faults in the northeast and northwest directions. The strata are scattered and broken, the crustal activity is strong, and the seismic intensity is VIII degrees. Landslide, collapse and debris flow are relatively developed.

Geological disasters in Gansu province are mainly distributed in Longnan mountainous area. This area belongs to the West Qinling Mountains, with high terrain in the west and low terrain in the east, with an altitude of 2500-4500m, strong terrain cutting, well-developed hydrological network, and relative elevation difference of 1000-2000m, belonging to the middle and high mountains. Rock and soil types are mainly metamorphic rocks and carbonate rocks, and clastic rocks and loess are scattered. The average annual rainfall is generally 600mm, and the rainfall from July to September accounts for 65% of the whole year, with heavy rain. Vegetation coverage rate is 30% ~ 46%. It belongs to the moderate-high-extreme development area of landslide and debris flow.

Analysis of Early Warning and Forecasting Effect in 5.8.2.3

On July 20th, the earthquake-stricken areas in southern Gansu, central Sichuan and north China were issued with 4 ~ 5 grade geological disaster warning and forecast. On July 2 1 ~ 22, a large number of geological disasters occurred, which actually occurred in southeastern Sichuan and southern Gansu. The local forecast in southern and central Gansu is accurate, while the forecast in northern Sichuan is inaccurate because the actual rainfall has shifted. The rainstorm centers predicted on the 20th are the hardest hit areas such as southern, central and northern Sichuan, but the actual rainstorm centers are located in southeastern Sichuan, southern Gansu and southwestern Shaanxi (Figure 5.49).

5.8.3 Analysis of Early Warning and Forecasting Effect in 2008

This chapter selects the forecast of July and August 2008 for analysis.

5.8.3. 1 successful prediction analysis

In actual calculation, if there are only 1 forecast areas on the same day, it will be calculated as 1 area; If there is more than one forecast area, it will be calculated according to the actual number of forecast areas, and the third, fourth and fifth level areas will participate in the calculation. The prediction accuracy of July and August 2008 is calculated by using the calculation formula established in Section 3.7 of Chapter 3 (Table 5. 1 1).

Fig. 5.49 Comparison of forecast rainfall, actual rainfall and distribution of geological hazards on July 2 1 day.

Table 5.11Forecast Accuracy in July and August 2008

Table 5. 1 1 lists 93 forecast areas released in July, and there are 30 accurate forecast areas, with an average forecast accuracy rate of 32.26%. In August, * * * released 64 forecast areas, including 14 accurate forecast areas, with an average forecast accuracy of 2 1.88%. The accuracy of daily forecast varies from 0 to 100%, which shows that the accuracy of geological disasters is random and has a certain relationship with rainfall. It is a complex process, which leads to low accuracy of forecast. When there is a large range of heavy rainfall, the forecast accuracy will be improved.

Analysis on the Present Situation of 5.8.3.2 Aeronautical News

In actual calculation, if there are only 1 empty areas on that day, it will be calculated as 1 empty area; If there is more than one empty report area, it will be calculated according to the actual number, and the third, fourth and fifth areas will participate in the calculation. The sum of false alarm rate and accuracy rate is 1. Using the calculation formula established in Chapter 3.7, the false report rate in July and August 2008 is calculated (Table 5. 12).

Table 5.12 Empty Reporting Rates in July and August 2008

According to the calculation results of false alarm rate in Table 5. 12, the average false alarm rate in July is 67.74%, and that in August is 78. 12%, which is relatively large, mainly because the forecast rainfall is quite different from the actual rainfall.

Table 5.13 Missed reporting rate in July and August 2008

From the forecast rainfall and actual rainfall on July 20th, 2008, it can be seen that in the two areas where 100mm is predicted, the rainfall in one area is less than 10mm, and the maximum rainfall in the other area is only 40 mm. The rainfall center is completely out of the forecast area, and the maximum rainfall in the rainfall center is 73mm, which is 27mm different from the forecast100mm..

Fig. 5.50 Comparison chart of forecast rainfall and actual rainfall on July 20th.

Investigation and Analysis of Missing Report in 5.8.3.3

Using the calculation formula established in Chapter 3.7, the missing rate in July and August 2008 is calculated (Table 5. 13).

According to the calculation results shown in Table 5. 13, the average missed detection rate is 66.87% in July and 86.54% in August, which is relatively high, mainly because the prediction accuracy of geological disasters caused by strong convective weather such as big clouds or typhoons is high, while the prediction accuracy is low for geological disasters caused by local rainstorm and other weather conditions.

5.8.4 Rainstorm Days and Geological Disasters

Superimpose the number of rainstorm days in flood season (May-September) with the distribution of geological disaster points (Figure 5.5 1).

It shows that the areas with large rainstorm days are concentrated in southern Guangdong, southern Guangxi and eastern Hubei. Fig. 5.52 segmentation of rainstorm days and statistics of geological disaster points per unit area show that the areas with high disaster point density are concentrated between 3 and 5 days of rainstorm days, but the regional geological disaster point density is not the largest, that is, the distribution of rainstorm days and the distribution of geological disaster point density do not have a good corresponding relationship as a whole.

Fig. 5.51distribution map of rainstorm days and geological disasters in China from May to September, 2008 (thematic data of Taiwan Province Province is temporarily missing).

Figure 5.52 Statistics of National Rainstorm Days and Geological Disasters per Unit Area from May to September, 2008

5.8.5 Analysis of Geological Disasters Caused by Strong Precipitation Process

In the flood season of 2008 (May-September), there were eight heavy precipitation processes in China, which caused a large number of geological disasters such as collapse, landslide and debris flow in areas prone to geological disasters.

(1) Heavy Rainfall Process on May 25th ~ 3rd, 20081day

On May 25th-3rd, 20081day, heavy precipitation occurred in most parts of southern China, especially in Guangxi, Guizhou and Guangdong, with the precipitation reaching 50-200mm, which has caused 365 major geological disasters in many provinces of China. Among them: Hunan 206, Guangxi 32, Guizhou 17 (Figure 5.53).

Fig. 5.53 Heavy precipitation process and distribution of geological disasters on May 25th ~ 3rd, 20081day (thematic data of Taiwan Province Province is temporarily missing).

As can be seen from the statistics of precipitation segmentation and the number of disaster points per unit area in Figure 5.54, the density of geological disaster points is relatively high when the process precipitation is within the range of 50 ~ 200mm, especially in the areas where the process precipitation is more than 200mm, which are mainly distributed in northeastern Guangxi and parts of northern Guangdong, and the distribution of geological disaster points is relatively concentrated, with the density of 7.4 points/100km2; The process precipitation 150 ~ 200mm covers the border areas of Guizhou and Guangxi provinces (regions), and the density is also high, reaching 2.8/150~200mm. According to national statistics, 88.8% of the geological disasters occurred on May 25th ~ 3rd1day, and the accumulated rainfall was 50 ~ 100 mm, which was mainly caused by this heavy precipitation process.

Figure 5.54 Statistics of precipitation segmentation and geological disasters per unit area from May 25th to May 30th, 2008.

(2) The heavy precipitation process on June 6, 2008 19.

On June 6 ~ 19, 2008, there was a continuous heavy precipitation process in most parts of southern China, especially in Guangdong, Guangxi and Jiangxi, where the precipitation reached 200 ~ 800 mm, and there were 596 disaster sites in many provinces across the country. Among them: Jiangxi 147, Guangxi 126, Hunan 88, Guangdong 55, Zhejiang 33 and Yunnan 23 (Figure 5.55).

Fig. 5.55 The heavy precipitation process and the distribution of geological disasters from June 6 to June 9, 2008 19 (thematic data of Taiwan Province Province is temporarily missing).

According to the statistics of precipitation segmentation and the number of disaster points per unit area in Figure 5.56, the process precipitation is in the range of 200 ~ 800 mm, and the geological disaster points are the most distributed, accounting for 70.5% of the total number of disaster points in China. The area with process precipitation above 800mm is mainly distributed in southeast Guangdong, which is an area where geological disasters are not easy to occur, and no disaster points appear; The area with process precipitation of 400 ~ 800 mm basically covers the mountainous areas (high-risk areas of geological disasters) in Guangdong, Guangxi, Jiangxi, Zhejiang, Anhui and other provinces (regions), and the geological disasters are most widely distributed, with the density of geological disasters of 4.6 ~ 6.4/ 100 km2. The area with process precipitation of 200 ~ 400 mm covers Yunnan, Chongqing, Hunan and other places, and geological disasters are widely distributed, with the disaster point density of 6.4/100km2. It can be seen that the occurrence of this large-scale geological disaster is mainly controlled by this heavy precipitation process.

Fig. 5.56 Statistics of precipitation period and geological disasters per unit area from June 6 to 19, 2008.

(3) The strong precipitation process on July 6th, 2008 10.

From July 6, 2008 to10, heavy rainfall occurred in most parts of South China, eastern Guizhou, central and western Jiangnan, eastern Jianghan, western Jianghuai, central and eastern Huanghuai and northern Jilin, and 76 major disaster spots occurred in many provinces across the country, including Guangdong 13, Hubei 13 and Anhui 9.

According to the statistics of precipitation segmentation and the number of disaster points per unit area in Figure 5.57, with the increase of process precipitation, the density of geological disaster points is obviously increasing, especially in the area where process precipitation is between 100 ~ 300 mm, and the density of geological disaster distribution points is 0.8/100km2; The area with process precipitation above 300mm is mainly distributed in southeast Guangdong, which is an area where geological disasters are not easy to occur, and no disaster points appear; The process precipitation is in the range of 0 ~ 0~ 100mm, and there are also a large number of disaster points. It can be seen that the heavy precipitation process is widely distributed, and there are still many disaster points in other precipitation areas except the number of disaster points in the precipitation center.

Figure 5.57 Statistics of precipitation period and geological disasters per unit area from July 6, 2008 to 10.

(4) The heavy precipitation process from July 20 to 24, 2008.

From July 20 to 24, 2008, there were heavy rains in Sichuan Basin, Huanghuai, Jianghuai and other places, with rainfall of 50-200mm, which caused a lot of geological disasters, including 50 in Sichuan, 29 in Hubei, 26 in Hunan, 7 in Shaanxi, 6 in Chongqing and 6 in Guizhou.

According to the statistics of precipitation segmentation and the number of disaster points per unit area in Figure 5.58, the regional process precipitation with the highest density of disaster points is mainly between 100 ~ 150 mm, mainly distributed in geological disaster-prone areas such as Sichuan, Hubei and Hunan, while the areas with higher process precipitation (> > 200mm) have relatively low density of disaster points, mainly because these areas are mainly located in Shandong. It can be seen that the occurrence of disasters in mountainous areas or geological disaster-prone areas is mainly controlled by the strong precipitation process, that is, geological disasters will occur in large numbers only if the strong precipitation process falls in the geological disaster-prone areas.

(5) The heavy precipitation process from July 3, 2008 to August 2, 2008.

From July 3/Kloc-0 to August 2, 2008, heavy rainfall occurred in Anhui and Jiangsu provinces, with a cumulative rainfall of 50-200 mm and a local rainfall of 250-530 mm. The largest rainfall center was located in the northeast of Anhui (> > 300 mm), and no disaster occurred. The secondary rainfall center is located in the south of Anhui, which is a disaster-prone area, causing 10 disasters.

Figure 5.58 Statistics of precipitation segmentation and geological disasters per unit area from July 20 to 24, 2008

The statistics of precipitation segments and the number of disaster points per unit area in Figure 5.59 also reflect this feature. The disaster points are mainly distributed in areas with process precipitation100 ~ 300mm. In other areas covered by 10 ~ 100 mm, some disaster points are scattered.

Fig. 5.59 Statistics of precipitation segmentation and geological disasters per unit area from July 3, 2008 to August 2, 2008.

(6) The heavy precipitation process from August 13 to August 17, 2008.

From August 13 to August 17, 2008, heavy rain and local heavy rain occurred in most areas such as the middle and upper reaches of the Yangtze River and Jianghuai, with rainfall generally above 50 mm, including southern and eastern Hubei, northwestern Hunan, southeastern Henan and western Anhui 100 ~ 200 mm, and some areas exceeded 200 mm. Among them, there are 27 in Hunan, 0/4 in Hubei/KLOC, 0/2 in Sichuan/KLOC, 6 in Guizhou, 3 in Shaanxi and 2 in Chongqing.

According to the statistics of precipitation segmentation and the number of disaster points per unit area in Figure 5.60, the area with the highest density of disaster points mainly falls in the area with precipitation greater than 200mm, because this area is located in the northwest of Hunan, and the precipitation intensity is greatly concentrated in [the 24-hour precipitation of mulberry planting in Hunan (164.4mm) and the passage (1 13.4mm).

(7) The heavy precipitation process on August 28th-29th, 2008.

On August 28-29, 2008, the cumulative rainfall in Hubei, Anhui, Chongqing and other places was generally 50-250 mm. There were 7 geological disasters in Hubei and 4 in Chongqing.

According to the statistics of precipitation segmentation and disaster points per unit area in Figure 5.6 1, the disaster points are mainly distributed in areas where the process precipitation is more than 50mm, mainly in Hubei, northern Hunan and most of Chongqing. The accumulated rainfall in two days basically reached the level of rainstorm, with high rainfall intensity and frequent geological disasters.

Figure 5.60 Statistics of precipitation time and geological disasters per unit area from August 13 to August 17, 2008.

Fig. 5.61Statistics of precipitation segmentation and geological disasters per unit area on August 28-29, 2008

(8) The heavy precipitation process from September 22 to 27, 2008.

From September 22 to 27, 2008, there were heavy rains in 9 counties (cities) in Sichuan Province. Heavy rain occurred in Beichuan County for five consecutive days; The daily precipitation in Pengshan and Xindu counties (cities) in September exceeded the historical extreme. Roads in some places in the earthquake-stricken areas were interrupted, landslides and mudslides occurred frequently, and there were 40 major disaster points (Figure 5.62). The area with the highest density of geological disasters is located in the area with precipitation 100 ~ 200mm, followed by the area with precipitation100 ~ 200mm.

According to the statistics of precipitation segmentation and the number of disaster points per unit area in Figure 5.63, the disaster points are mainly distributed in the area of process precipitation 100 ~ 200 mm, mainly extending in the north-south direction of western Sichuan.

5.8.6 Analysis of geological disasters caused by typhoon and rainstorm

In the flood season of 2008 (May-September), six typhoons landed in Chinese mainland, which brought abundant precipitation and played a certain role in the occurrence of geological disasters such as collapse, landslide and debris flow.

(1) Tropical Storm Fengshen (25-29 June)

Tropical Storm Fengshen No.6 landed in Shenzhen on the morning of June 25th. Affected by this, heavy rains in Guangdong, Fujian, Guangxi, Jiangxi, Hunan and other places have caused a large number of geological disasters such as collapses, landslides and mudslides in Guangdong, Jiangxi, Zhejiang and Guangxi.

Judging from the density of disaster points in different precipitation periods, when the process precipitation is between 50 and 400 mm, there are many disaster points, especially when the process precipitation is between100 and 200 mm and 300-400 mm, the density of disaster points reaches 1.2/100km2 and1respectively. Areas with precipitation greater than 400mm are mainly concentrated in the southeast coastal areas of Guangdong, and disasters are rare (Figure 5.64). The geological disasters in this period were mainly caused by the concentrated precipitation brought by typhoons.

Fig. 5.62 Distribution map of heavy precipitation process and geological disasters on September 22-27, 2008 (thematic data of Taiwan Province Province is temporarily missing).

Figure 5.63 Statistics of precipitation segmentation and geological disasters per unit area from September 22 to 27, 2008

Figure 5.64 Distribution Statistics of Disaster Points of Tropical Storm Fengshen (June 25th-29th)

(2) Tropical storm "Seagull" (July 19 ~ 20)

Tropical Storm No.7 "Seagull" was formed in the east of the Philippines on the afternoon of July 15. It landed in Yilan County, Taiwan Province Province on June 38+07, and landed in Xiapu County, Fujian Province again on June 38+08. Affected by this, heavy rains in Fujian, Guangdong, Zhejiang, Jiangxi and other places caused 7 small disasters such as landslides, collapses and mudslides in Guangdong and Fujian provinces (Figure 5.65).

Fig. 5.65 Distribution Statistics of Disaster Points Caused by Tropical Storm "Seagull" (July 19 ~ 20)

This precipitation process has the characteristics of relatively concentrated precipitation areas, the area with process precipitation greater than 50mm is small, and the disaster points are concentrated in the local area with process precipitation100 ~150 mm.

(3) Tropical Storm Phoenix (July 28th to August 2nd)

Tropical storm No.8 "Phoenix" was generated in the afternoon of July 25th, and landed in Hualien City, Taiwan Province Province on the morning of 28th, and landed again in Fuqing City, Fujian Province at 22: 00 on the same day, with typhoon intensity (wind force near the center 12). Affected by it, heavy rains have fallen in southeastern Zhejiang, central and northern Fujian and other places, and some areas have heavy rains or heavy rains; Strong winds of 8 ~ 10 occurred in the Yangtze estuary, Fujian, Zhejiang and other places, reaching 14 locally. In Anhui, Fujian, Guangdong, Jiangxi and other provinces, 35 cluster geological disasters have been triggered.

The areas with process precipitation above 300mm are mainly concentrated in the border area between eastern Anhui and Jiangsu, which belongs to the areas where geological disasters are not easy to occur, and there is no distribution of disaster points. The areas with process precipitation 100 ~ 300mm are mainly distributed in areas with frequent geological disasters such as Fujian, Guangdong and southern Anhui, with concentrated precipitation, fragile geological background and environmental conditions, and a large number of geological disasters occur (Figure 5.66).

Fig. 5.66 Distribution statistics of disaster points induced by tropical storm Phoenix (July 28th to August 2nd)

(4) Severe tropical storm "Beimian" (August 7-9)

The severe tropical storm "Beimian" landed on the coast of Yangxi County, Guangdong Province on the evening of August 6, with the maximum wind force near the center 10. On the afternoon of the 7th, it landed again along the coast of dongxing city, Guangxi, with a maximum wind force of 8 near the center. Affected by it, most of South China and Yunnan experienced heavy rain, local heavy rain or torrential rain, and the maximum precipitation in the process exceeded 400 mm, causing geological disasters 130, including 50 in Sichuan, 29 in Hubei, 26 in Hunan, 7 in Shaanxi, 6 in Chongqing and 6 in Guizhou.

Judging from the density of disaster points in the process of precipitation segmentation, the areas with precipitation greater than 200mm are distributed in some areas in southern Guangxi, and the geological disasters are low. Areas with precipitation of 50 ~ 100 mm are distributed in disaster-prone areas such as eastern Yunnan, central Guangxi and central Guangdong, and the density of disaster points reaches 1.4/100km2 (Figure 5.67).

Fig. 5.67 Distribution statistics of disaster points of severe tropical storm "Beimian" (August 7 -9)

(5) Strong typhoon Senlake (September 14 ~ 16)

The strong typhoon "Senlake" landed on the coast of Yilan County, Taiwan Province Province in the early morning of September 14, and the maximum wind force near the center was 15 (48m/s) when landing. "Senlake" has the characteristics of rapid development, strong intensity, slow movement, abnormal path, frontal attack on Taiwan Province Province and long influence on Taiwan Province Province and the East China Sea. Precipitation is concentrated in the northeast coast of Fujian and the southeast coast of Zhejiang, and there is no typical typhoon disaster report (Figure 5.68).

Fig. 5.68 Statistics of disaster points caused by the strong typhoon Senlake (September 14 ~ 16).

(6) Strong typhoon Hagupit (September 23-27)

The strong typhoon "Hagupit" landed on the coast of Dianbai County, Guangdong Province on the morning of September 24th, and the maximum wind force in the center reached 15 (48m/s) when landing. The process of heavy precipitation brought by Hagupit is similar to the severe tropical storm "Beimian". The precipitation in the area with the highest density of geological disaster points is between100 ~ 200mm, which has caused a large number of geological disasters in Guangdong, Guangxi and Yunnan (Figure 5.69).

Figure 5.69 Statistics of distribution of disaster points caused by strong typhoon Hagupit (September 23rd to 27th).

5.8.7 Comparison between the first and second generation regional early warning systems.

According to the spatial forecast accuracy of July-August 2007 and July-August 2008, the former is about 40% and the latter is about 27%, but the early warning area of the latter is only one quarter of the former, which greatly reduces the early warning area, which is equivalent to reducing the corresponding disaster prevention cost.

Two systems are used to compare and analyze the actual early warning situation from May 1 day to May 15, 2008 (Table 5. 14).

Table 5.14 Comparison of the first and second generation regional early warning systems in flood season in 2008

The conclusion is that the second-generation early warning system, on the basis of inheriting the advantages of the first-generation system in judging critical rainfall, highlights the regional geological environment conditions and greatly improves the accuracy and fineness of early warning.